Why isn't organ donation obligatory?

I kind of understand what you are saying but at the time, I think people should have a choice whether to donate their organs or not. Yes it may be selfish but, most people would like to die intact regardless of the fact that the body just rots in the ground or is turned to ashes. It maybe perceived as selfishness or laziness but it's a right we have whether to do it or not. I don't think forcing people is the answer.